1. Field of the Invention
The present invention relates generally to a paging method in a mobile communication system, and in particular, to a method for supporting fast paging by changing a paging channel monitoring cycle for a mobile station (MS).
2. Description of the Related Art
In a code division multiple access (CDMA) system, an MS monitors a channel to receive a message or data from a base station (BS). The channel monitoring is carried out in a non-slotted mode or in a slotted mode. The channel is continuously monitored in the former, while it is monitored only periodically at predetermined points of time in the latter. Due to the continuous channel monitoring, the non-slotted mode operation leads to large battery consumption in the MS. To save battery power, the MS typically operates in the slotted mode when it is in an idle state. In the slotted mode, the MS monitors a paging channel at a predetermined cycle of one or two slots. The paging channel monitoring period is determined by a slot cycle index (SCI).
To determine the SCI, the MS first notifies a BS of an intended slot cycle through an Origination Message, a Registration Message, or a Page Response Message. The BS tells the MS a maximum available SCI (MAX_SLOT_CYCLE_INDEX) through a System Parameter Message (SPM) or an MC-RR Parameter Message (MCRRPM). Each time the MS receives the SPM or MCRRPM, the MS updates its SCI value (SLOT_CYCLE_INDEXs) to the lesser of the MAX_SLOT_CYCLE_INDEX and its desired SCI (SLOT_CYCLE_INDEXp). That is, the MS determines the lesser of the MAX_SLOT_CYCLE_INDEX and the SLOT_CYCLE_INDEXp as the SLOT_CYCLE_INDEXs. In actual operation, the MS can use a value less than or equal to the SLOT_CYCLE_INDEXs as the SCI.
The SCI can vary due to many factors. Since SLOT_CYCLE_INDEXp is an internally stored value in the MS, the user of the MS can intentionally change the value. Also, each BS may set a different value as the MAX_SLOT_CYCLE_INDEX. Hence, as the MS moves to another BS, system or network, the SCI available to the MS can be changed. The change of the SCI entails parameter change registration.
In a group call service, a push-to-talk (PTT) function allows a portable terminal to take on a walkie talkie type functionality through shortening of a call connection time where a user is able to set up a one-to-one or one-to-multiparty connection between portable terminals. Chatting and instant messaging are examples of the PTT service. The implementation of the PTT service requires fast call setup. To fast respond to a BS request, the MS needs to continuously monitor the paging channel. The non-slotted mode paging channel monitoring enables a fast response, but it nonetheless consumes much power relative to the slotted mode operation. As a result, the battery of the MS runs out of power in a shorter time. However, the conventional slotted mode operation reduces the battery power consumption but makes the MS respond slowly.
In this context, the BS can allow the MS to operate with a desired SCI in a reduced slot cycle (RSC) mode. The RSC mode was introduced in CDMA2000 Release D. It can expand the SCI even to a negative number. That is, the SCI can be set to one of “−4, −3, −2, −1, 0, 1, 2, 3, 4, 5, 6, 7”. If it is set to −4, the MS monitors the paging channel every slot.
Traditionally, to change the SCI, the MS indicates its desired SCI through the Origination Message, the Registration Message or the Page Response Message. Or, the MS transmits the SCI through a Release Order when transitioning from a traffic state to a release state. There are no other alternatives.
That is, the BS can neither intentionally change the SCI of the MS nor adjust the SCI when the MS is in an idle state.